Vehicles operating in an autonomous mode (e.g., driverless) can relieve occupants, especially the driver, from some driving-related responsibilities. When operating in an autonomous mode, the vehicle can navigate to various locations using onboard sensors, allowing the vehicle to travel with minimal human interaction or in some cases without any passengers.
Motion planning and control are critical operations in autonomous driving, including speed control and steering control of an autonomous driving vehicle (ADV). In conventional steering control of the ADV, a rear axle is utilized as a control reference for steering. Typically, a global positioning system (GPS) sensor or receiver is located near the rear axle and the rear axle is considered as a position of the ADV. Any control command such as speed control commands or steering control commands will be determined based on the rear axle as a control reference.
However, in steering control of an ADV, using the real axle as a control reference may cause understeering at least at the beginning of turning as shown in FIG. 1A. The control system of the vehicle always tries to align the control reference on the real axle to the planned route, especially during steering control of the vehicle. As shown in FIG. 1A, due to the steering control based on the rear axle, the front portion of the vehicle is understeering by drifting off the planned steering route. The turning of the front portion of the vehicle may be delayed and the vehicle may overcorrect such understeering later on. The passengers sitting upfront may also feel uncomfortable as a result.